Multi-band, multi-mode spread-spectrum communication system

ABSTRACT

A technique for spread-spectrum communication which uses more than one mode and more than one frequency band. Selectable modes include narrowband mode and spread-spectrum mode, or cellular mode and microcellular mode. Selectable frequency bands include both licensed and unlicensed frequency bands, particularly frequency bands including the 902-928 MHz, 1850-1990 MHz, and 2.4-2.4835 GHz frequency bands. Spread-spectrum communication channels are 10 MHz or less in width. The frequency band onto which spread-spectrum signals are encoded may be changed upon a change in environment or other control trigger, such as establishment or de-establishment of communication with a private access network. A multi-band transmitter comprises a single frequency synthesizer and a frequency source (e.g., a local oscillator), coupled to a selectable band pass filter. A multi-band receiver capable of monitoring one or more frequency bands comprises bank of bandpass filters and a demodulator comprising a single frequency synthesizer and a frequency source.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of application Ser. No.08/293,671 filed on Aug. 18, 1994, which is in turn acontinuation-in-part of application Ser. No. 08/146,492 filed on Nov. 1,1993 abandoned, and application Ser. No. 08/059,021 filed May 4, 1993abandoned, (which is a continuation-in-part of Ser. No. 07/976,700 filedNov. 16, 1992 and application Ser. No. 08/206,045 filed on Mar. 1, 1994abondoned, (which is a continuation of Ser. No. 07/948,293 filed on Sep.18, 1992, and now issued as U.S. Pat. No. 5,291,516, which is afile-wrapper continuation of Ser. No. 07/698,694 filed May 13, 1991,each of which is hereby incorporated by reference as if fully set forthherein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to spread-spectrum communication and, moreparticularly, to a communication system using multiple communicationmodes over multiple frequency bands.

2. Description of Related Art

Cellular telephony has been well known for many years, but with itsgrowing popularity, more channels in the allocated cellular frequencieshave become necessary. Among the proposed advances in the art have beena move from frequency division multiple access (FDMA) systems usingnarrowband analog communication to digital voice communication usingtraditional narrowband FDMA techniques possibly coupled with timedivision multiple access (TDMA) techniques. Further proposed advancesinclude the use of code division multiple access (CDMA) techniques suchas spread spectrum systems. Examples of communication protocols includeIS-45, IS-95, DCS1900 (otherwise known as GSM), DECT (Digital EuropeanCordless Telephone), and AMPS.

Another approach to the problem of allowing increased numbers of usersin a geographic location is the concept of personal communicationssystems, or PCN's, which utilize microcells. A microcell is similar to acell in a traditional cellular system, except much smaller. Where atraditional cell may cover an area of several square miles, a microcellmay only be a few hundred feet in diameter. By limiting transmit power,more microcells, and thus more users, may be co-located in a geographicarea.

Prior art does not teach a method for operation of a single telephonewhich has the ability to function both as a narrowband frequency, time,and/or code division multiplexed cellular phone, as well as amicrocellular telephone utilizing time, frequency, or code divisionmultiplexing, where the cellular and microcellular functions eithershare the same frequency bands of operation or are offset from eachother. Nor does the prior art teach such a system where themicrocellular mode may employ a paging unit independent of the unit'stelephone functionality.

For purposes of the present specification, "analog voice" is describedas a system where an analog voice system directly modulates a radiofrequency (RF) carrier or intermediate frequency (IF) signal, anddigital voice is described as a system where the signal is firstdigitized, and possibly compressed through any number of methods commonand well known in the art, and whose digital signal is then used for RFcarrier or IF modulation. A narrow band modulation typically usesamplitude modulation (AM) or frequency modulation (FM), and has abandwidth between 3 kHz and 30 kHz.

In spread-spectrum communication, the spread-spectrum signal which isgenerated and transmitted has a spreading bandwidth which exceeds thebandwidth of the data stream. When using spread-spectrum techniques forwireless communication, it may be necessary to avoid or minimizeinterference with other users of the electromagnetic spectrum. Someexamples of such other users are microwave communication users (such asthe Operational Fixed Services ("OFS") using microwave communicationtowers) and cellular communication users (such as those using cellulartelephones). In particular, OFS services are critical to controlling,among other things, the nation's electric power grid, which makes thepossibility of inadvertent OFS disruption extremely serious.Accordingly, it would be advantageous to avoid or minimize interferencewith microwave and cellular communication users.

In wireless communication, the transmitted signal may be subject tovarious forms of frequency-selective fading, which may cause the signalto fade or drop out over a localized range of frequencies. Althoughspread-spectrum signals are distributed over a wider range offrequencies than narrowband signals, they may also be subject tofrequency-selective fading over a portion of their spreading bandwidth.Accordingly, it would be advantageous to mitigate the effect offrequency-selective fading.

Spread-spectrum modulation in more than one frequency band can bedifficult due to the wide separation between frequency bands. Forexample, operation in the 900 megahertz and 1800 megahertz bands couldrequire a synthesizer capable of covering approximately 1,000 megahertzin frequency spectrum. However, in hand-held equipment such astelephones, it is undesirable to use more than one synthesizer, or evenmore than one oscillator, due to increased cost, weight, and relatedconsiderations. Accordingly, it would be advantageous to provide aspread-spectrum system in which a single, relatively narrow, synthesizerwould serve more than one operating frequency band.

SUMMARY OF THE INVENTION

The invention provides in one aspect a transmitter and receiver capableof operating in a plurality of frequency bands and/or in a plurality ofmodes, making use of either narrowband or spread-spectrum communicationtechniques. The invention may be embodied as a cellular or cordlesstelephone which utilizes frequency division multiplexing, time divisionmultiplexing, code division multiplexing, or various combinationsthereof. In one embodiment, the invention possesses both cellular andmicrocellular functionality, wherein transmission and/or reception mayoccur using either narrowband or spread-spectrum signals in conjunctionwith either FDMA, TDMA, or CDMA techniques, or any combination thereof.A system in accordance with the present invention may have two or moremodes, such as a cellular mode and a microcellular mode, or such as aspread-spectrum mode and a narrowband mode, and the various modes mayoccupy common frequency bands, overlapping frequency bands, or distinct,offset frequency bands.

Another aspect of the invention provides a technique for spread-spectrumcommunication which reduces interference from microwave and cellularcommunication users, especially when transmitting in a communicationband generally used by those users. In particular, said embodimentprovides a spread-spectrum technique having a spreading bandwidth ofabout 10 MHz or less, in combination with a known center frequency. Theknown center frequency may be within a microwave communication band or acellular communication band.

Another aspect of the invention provides a technique for spread-spectrumcommunication which uses more than one frequency band, particularlyunlicensed frequency bands, including the 902-928 MHz, 1850-1990 MHz,and 2.4-2.4835 GHz frequency bands, and including the 1910-1930 MHzfrequency band or other future unlicensed frequency bands. In saidembodiment, the frequency band onto which spread-spectrum signals areencoded may be changed upon a change in environment or other controltrigger, such as establishment or de-establishment of communication witha private access network.

The invention may be embodied as a transmitter generally comprising aswitch, a tunable-frequency synthesizer, one or more modulators, adual-band power amplifier (where the dual modes occupy distinctfrequency bands) or a single-band power amplifier (where the dual modesoccupy single, contiguous, or closely placed distinct bands), and anadjustable bandpass filter. The switch may be used to select eithernarrowband or spread-spectrum modulation, or may be used to select oneof a plurality of frequency bands for transmission. If narrowband modeis selected, a narrowband modulator modulates an input signal, combinesit with a carrier frequency generated by the tunable frequencysynthesizer, and provides an output to the power amplifier and theadjustable bandpass filter for transmission. If spread-spectrum mode isselected, the input signal is provided to a spread-spectrum modulatorfor generating a spread-spectrum signal. The spread-spectrum signal iscombined with a carrier frequency generated by the tunable frequencysynthesizer and provided to the power amplifier and the adjustablebandpass filter for transmission. The adjustable bandpass filter may betuned, and the power amplifier switched, where distinct, offsetfrequencies are employed for the two operating modes.

The invention may also be embodied as a receiver generally comprising aswitch, a tunable-frequency synthesizer, a tunable bandpass filter, apreamplifier, a frequency converter, an IF amplifier, and one or moredemodulators. The receiver generally operates in reverse fashion fromthe transmitter, whereby the mode select switch is used to selectbetween narrowband or spread-spectrum reception. If in narrowband mode,the adjustable bandpass filter may be adjusted to a narrow bandwidth forpassing a received narrowband signal, while in a spread-spectrum modethe adjustable bandpass filter may be adjusted to a wide bandwidth forpassing a received spread-spectrum signal. The bandpass filter also istunable, where different frequencies are utilized for distinct modes,and the preamplifier may also be switch selected or tuned to theappropriate band where the dual modes employ distinct, separatedfrequency band. The received signal is converted to an IF signal using alocal oscillator signal from the tunable-frequency synthesizer, and theIF signal is demodulated by either the spread-spectrum demodulator orthe narrowband demodulator depending on the chosen mode.

The invention further provides in another aspect a dual-bandspread-spectrum modulator which uses a single, relatively narrow,synthesizer to serve two operating frequency bands. In the lowerfrequency band, the synthesizer may operate in a high-side injectionmode, while in the higher frequency range, the synthesizer may operatein a low-side injection mode. In one embodiment, the lower frequencyrange may comprise about 1850 to 1990 megahertz, while the higherfrequency range may comprise about 2400 to 2483.5 megahertz.

Additional objects and advantages of the invention will be set forth inpart in the description which follows, and may be obvious from thedescription or learned by practice of the invention. The objects andadvantages of the invention also may be realized and attained by meansof the instrumentalities and combinations particularly pointed out inthe appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate preferred embodiments of theinvention, and together with the description serve to explain theprinciples of the invention.

FIG. 1 is a block diagram of a spread-spectrum communication transmitterand receiver;

FIG. 2 is a block diagram of a dual-mode transmitter according to theinvention;

FIG. 3 is a block diagram of a dual-mode receiver according to thepresent invention;

FIGS. 4 and 5 are illustrations comparing exclusion zones around amicrowave beampath;

FIG. 6 is a diagram of triangular cells arranged in a grid pattern;

FIG. 7 is a diagram of a triangular cell;

FIGS. 8 and 9 are diagrams showing an allocation of frequency bands;

FIG. 10 shows a dual-mode spread-spectrum modulator with two frequencybands;

FIG. 11 shows a programmable frequency generator;

FIG. 12 is a block diagram showing an alternative embodiment of atransmitter using a single frequency synthesizer for communicating overa plurality of frequency bands;

FIG. 13 is a block diagram showing another alternative embodiment of atransmitter using a single frequency synthesizer for allowingcommunication over a plurality of frequency bands;

FIG. 14 is a block diagram of a receiver using a single frequencysynthesizer for demodulating signals that may be sent over more than onefrequency band; and

FIG. 15 is a diagram of frequency bands and sub-bands illustratingfrequency pairs that may be generated by the transmitters shown in FIGS.11, 12 or 13.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the present preferredembodiments of the invention, examples of which are illustrated in theaccompanying drawings, wherein like reference numerals indicate likeelements throughout the several views. The disclosure of the inventionmay be supplemented by the contents of technical information appended tothis specification in a technical appendix, hereby incorporated byreference as if fully set forth herein. No admission is made as topossible prior art effect of any part of the appendix.

Modern and proposed cellular telephone systems currently utilize highpower, frequency, time, and/or code division multiplexed narrowbandradio frequency communication techniques in conjunction with large cellsto establish and maintain telephone communications. With the growingpopularity of these systems, increased user capacity is required withina geographical area. One approach to providing increased capacity ismicrocells, which utilize comparatively much smaller cells as well aslow power radio frequency techniques.

Traditional cellular systems have proven to be highly capital intensivein base station installations, on the order of several hundred thousanddollars per cell site, and therefore demand high operational and accessfees. Proposed microcell systems would require a much lower capitalinvestment per cell at a small fraction of cellular site installationcost, such that shop owners and other small operators could have a cellsite easily installed on their premises. Microcells potentially may belocated in public access areas, airports, restaurants, shopping malls,banks, service stations, etc., as well as commercial or officefacilities (utilizing wireless PBX, centrex, or key systems), andresidential sites. A microcell user, thus, could utilize the samehandset at home, in the office, or at most other public places where heor she typically would need access to telephone communications, in acost effective way, and maintain a single telephone number. Publicoperational and access charges to the user could then be much lower,likely on the order of pay phone charges per call, not per minute.

A disadvantage of microcellular systems is their potential lack ofincoming call accessibility. Potentially, one cannot place a call intothe system to the remote user. Studies have been performed, however,that estimate that up to 80% of all calls made in traditional cellularsystems are from the user outbound from the microcell user, and notinbound to the user. Even with no inbound access to the wirelessmicrocell user, a potentially large market exists which has little needfor incoming access, where users would be willing to surrender incomingcall access for the savings of a microcellular pager in the microcellhandheld unit, which can provide for a level of incoming access to theuser in the public environment.

Another disadvantage of microcells is practical handoff capabilitiesfrom cell to cell. Since the cells in a microcell system are small, thesystem becomes impractical to use from a moving vehicle since the userpotentially could be passing through cells every few seconds, makinghandoffs impractical. Microcellular systems may be designed such thatthere is no handoff capability between cells, which would provide for awireless pay phone type of system. Since microcells are so small, systemuse in remote areas would be impractical due to the number of cellinstallations necessary to provide complete coverage.

The present invention provides, in one embodiment, a dual-modetransmitter and receiver which achieves advantages of both systems, i.e.the range and mobility of traditional cellular, and the low cost ofmicrocellular. The dual-mode transmitter and receiver include adual-mode cordless telephone which has as its first mode operationalcapabilities which allow cellular functionality, and a second mode whichallows for micro-cellular operation. Functionality in the first, orcellular, mode includes a relatively high power cellular telephoneemploying analog or digital voice techniques in conjunction withfrequency, and/or time division traditional narrowband radio techniques.Functionality in the second, or microcellular, mode includes a low powermicrocellular telephone using digital voice techniques in conjunctionwith frequency, time and/or code division spread spectrum radiotechniques, where the cellular and microcellular functions either sharethe same frequency bands, or are offset from each other.

FIG. 1 shows a block diagram of a spread-spectrum communicationtransmitter and receiver.

A spread-spectrum transmitter 1 comprises an input port 2 for input data3, a chip sequence transmitter generator 4, and a transmitting antenna 5for transmitting a spread-spectrum signal 6. A spread-spectrum receiver7 comprises a receiver antenna 8, a chip sequence receiver generator 9,and an output port 10 for output data 11. A chip sequence 12 may beidentically generated by both the transmitter generator 4 and thereceiver generator 9, and appears essentially random to others notknowing the spreading code upon which it is based. The spread-spectrumsignal 6 may have a spreading bandwidth which exceeds the bandwidth ofthe input data 3. The spread-spectrum signal 6 may also be modulatedonto a communication channel having a center frequency, with the centerfrequency and the spreading bandwidth substantially defining acommunication channel. The communication channel may also have a knownsignal dropoff for energy outside the limits of the channel. Anextensive discussion of spread-spectrum communication, spreading codes,and chip sequences, may be found in R. Dixon, SPREAD-SPECTRUM SYSTEMS(2d ed. 1984).

In the exemplary arrangement shown in FIG. 2, a dual-mode transmitter inaccordance with various aspects of the present invention is showncomprising an antenna 109, a mode controller 103, a mode select switch104, transmitter-information processing means 101, a tunable-frequencysynthesizer 105, a chip-code generator 107, a spread-spectrum modulator111, a narrowband modulator 113, a power amplifier 115, and anadjustable bandpass filter 117. The transmitter-information means may beembodied as an information device 101. The information device 101 mayinclude source encoders such as Golay encoders, error correction coding,analog-to-digital converters, etc.

The spread-spectrum modulator 111 is coupled to the information device101 through mode select switch 104, the tunable-frequency synthesizer105 and the chip-code generator 107. The narrowband modulator 113 iscoupled to the information device 101 through mode select switch 104,and the tunable-frequency synthesizer 105. The power amplifier 115 iscoupled to the mode controller 103, the spread-spectrum modulator 111and the narrowband modulator 113. The adjustable, tunable, bandpassfilter 117 is coupled to the antenna 109, the power amplifier 115 andthe mode controller 103.

Narrowband or spread-spectrum modulation is selected using the modecontroller 103. The information device 101 processes the inputinformation signal, while the tunable-frequency synthesizer 105generates a carrier signal, and the chip-code generator 107 generates achip-code signal.

The mode controller 103 controls a mode select switch 104 which directsthe processed information signal to the narrowband modulator 113 or thespread-spectrum modulator 111. The spread-spectrum modulator 111modulates the carrier with the processed information signal and thechip-code signal as a spread-spectrum signal, when the mode selectswitch 104 has been selected for spread-spectrum modulation. Thenarrowband modulator 113 modulates the carrier with the processedinformation signal as a narrowband modulated signal, when the modeselect switch 104 is selected for narrowband modulation.

When the mode controller 103 is set to narrowband modulation, the poweramplifier 115 amplifies the narrowband modulated signal. Where the dualmodes function in distinct frequency bands, the power amplifier 115 mayeither be wideband enough to function in both bands, or may beadjustable to function in the band pertaining to the mode in operation,with mode controller 103 controlling its operation accordingly. When themode controller 103 is set to spread-spectrum modulation, the poweramplifier 115 amplifies the spread-spectrum signal. Similarly, with anarrowband modulation setting of the mode controller 103, the adjustablebandpass filter 117 has a bandwidth adjusted to a narrow bandwidth andcorresponding frequency for passing the narrowband modulated signal.With a spread-spectrum setting of the mode controller 103, theadjustable bandpass filter 117 has a bandwidth adjusted to a widebandwidth and corresponding frequency for passing the spread-spectrumsignal.

The present invention, as illustrated in FIG. 3, also includes anembodiment as a dual-mode receiver. The dual-mode receiver may comprisea mode controller 103, a tunable-frequency synthesizer 105, a chip-codegenerator 107, an antenna 109, an adjustable bandpass filter 117, apreamplifier 205, a frequency converter 209, an IF amplifier 211, a modeselect switch 104, a spread-spectrum despreader 215, a spread-spectrumdemodulator 217, a narrowband demodulator 213, and receiver-informationprocessing means. The receiver-information means is embodied as areceiver-information processing device 219. The adjustable bandpassfilter 117, is coupled to the antenna 201 and to the mode controller103. The preamplifier 205 is coupled to the adjustable bandpass filter117 and to the mode controller 103. The frequency converter 209 iscoupled to the preamplifier 205 and the tunable-frequency synthesizer105. The IF amplifier 211 is coupled to the frequency converter 209. Thespread-spectrum despreader 215 is coupled to the chip-code generator 107and through the mode select switch 104 to the IF amplifier 211. Thespread-spectrum demodulator 217 is coupled to the spread-spectrumdespreader 215. The narrowband demodulator 213 is coupled through themode controller 103 to the IF amplifier 211.

As with the dual-mode transmitter of FIG. 2, the mode controller 103 isused to select reception of narrowband or spread-spectrum modulation.The tunable-frequency synthesizer 105 generates a local oscillatorsignal, and the chip-code generator 107 generates a reference chip-codesignal for comparison with the received chip code signal.

When the mode controller 103 is set to narrowband modulation, theadjustable bandpass filter 117 is adjusted to a narrow bandwidth andcorresponding frequency for passing the narrowband modulated signal.With a spread-spectrum setting of the mode controller 103, theadjustable bandpass filter 117 is adjusted to a wide bandwidth andcorresponding frequency for passing the spread-spectrum signal. Thepreamplifier 205 amplifies the filtered narrowband modulated signal whenthe mode controller 103 is set to the narrowband modulation setting, andamplifies the filtered spread-spectrum signal when the mode controlleris set to the spread-spectrum modulation setting and is switchselectable to the appropriate band for each mode where the dual modeoccupy non-contiguous or widely separated frequency bands. The frequencyconverter 209 converts using the local oscillator signal, the filterednarrowband modulated signal and the filtered spread-spectrum signal toan IF signal.

FIGS. 2 and 3 illustrate the implementation of a dual-band, dual-modetransmitter and receiver, respectively, for use in any narrowbandapplication with capability to switch to a separate frequency band whileemploying spread spectrum modulation/demodulation in the alternateoperating band.

Operation of the dual-band transmitter of FIG. 2 is as follows. Usingtransmitter-information processing device 101, input information may befiltered, analog-to-digital (A/D) converted if required, as determinedby the mode switch control, and applied to either a narrowband or spreadspectrum modulation process. Narrowband modulation is employed in anarrowband mode and spread spectrum modulation employed in aspread-spectrum mode. In either mode, the modulated carrier is appliedto the dual-band RF power amplifier 115.

The tunable frequency synthesizer 105, which provides the proper carrierfor either conventional narrowband or spread spectrum mode, iscontrolled by the mode switch controller 103, outputting only one ofpossibly many required transmit carrier frequencies for modulation atany one time.

After amplification, the proper modulated carrier signal, eitherconventional narrowband or spread spectrum, is applied to an adjustable,tunable bandpass filter 117 and then to the antenna 109. The pass bandand frequency of the adjustable bandpass filter 117 is selected by themode controller 103. This is necessary to meet transmission spurioussignal level control standards.

A single, dual-band antenna 109 then acts as a transducer to convert theelectrical RF signal from the power amplifier 115 and adjustablebandpass filter 117 to an electromagnetic signal for propagation to thereceiver.

The mode controller 103 also controls the operation of a reference codegenerated by chip-code generator 107. The reference code is used as aspectrum-spreading function in the spread spectrum mode. The chip-codegenerator 107 would not operate in the conventional narrowband mode.

This transmitter configuration is applicable to any desired dual modesystem in which one mode is used in a conventional narrowband system,such as cellular telephones, while a second mode is employed forcommunicating with a spread spectrum system.

Receiver operation of the receiver in FIG. 3 is as follows. A receivedsignal is converted by the antenna 109 from an electromagnetic signal toan electrical signal. The antenna 109 may or may not be common to thetransmitter. The received signal is then applied to an adjustablebandpass filter 117, which may or may not be common to the transmitter,and which is controlled by the mode controller 103. The adjustablebandpass filter 203 selects the proper conventional narrowband or spreadspectrum operating signal and passes it through a preamplifier 205,whose output is applied to a frequency converter 209.

The other input to the frequency converter 209 is a local oscillatorsignal generated by a tunable frequency synthesizer 105 whose frequencyin turn is controlled by the mode controller 103. The input signal isconverted to an intermediate frequency (IF), which may be the same foreither conventional narrowband or for spread spectrum signals. Thereceiver is assumed to be the superheterodyne type, and is illustratedas a single conversion receiver, but may also be implemented by a dualor multi-conversion superheterodyne receiver without a change in theoverall system's operation.

An output signal from the frequency synthesizer 105 is multiplied withthe amplified input signal from the preamplifier 205 selected by theinput filter, in frequency converter 209 to produce the intermediatefrequency signal. A tuned, fixed frequency IF amplifier 211 amplifiesthe received signal and applies it to a mode select switch 104 whoseoutput is coupled to either the conventional narrowband signaldemodulator 213 or the spread-spectrum signal despreader 215. Thedespreader 215 uses a reference code provided by the chip-code generator107 to facilitate proper spread spectrum signal selection anddespreading. This reference code is controlled by the mode controller103, and may be common to the transmitter shown in FIG. 2.

The spread-spectrum despreader 215 despreads, using the referencechip-code signal, the IF signal as a digitally modulated signal. Thespread-spectrum demodulator 217 demodulates the digitally modulatedsignal as a digitally demodulated signal. The narrowband demodulator 213demodulates the filtered narrowband modulated signal as a demodulatedsignal. The receiver-information device 219 processes the demodulatedsignal as an information signal.

Spread spectrum signals, after being despread, are demodulated by aspread-spectrum demodulator 217, separate from the narrowbanddemodulator 213. This is necessary because of the difference inconventional signal information modulation of the carrier is typicallyanalog FM, while spread spectrum signals may employ digital modulationand may be digital-to-analog (D/A) converted prior to processing. If thenarrowband technique used employs digital modulation, a secondnarrowband D/A demodulator, similar to the spread spectrum demodulator,may be employed, or the spread spectrum demodulator may be eliminatedand D/A demodulation, which may be identical for both narrowband andspread spectrum modulation, may be included as a function of thereceived information processor.

After despreading, spread-spectrum demodulator 217 output signals areprocessed, using receiver-information device 219, by filtering,digital-to-analog conversion, and amplification, as necessary, toconvert it to a form that is usable to the information outputdestination. Processing is selected by the mode switch control 103.

As in the transmitter of FIG. 2, more than two modes can be supported bythe same general receiver configuration of FIG. 3. This includesoperation at multiple frequencies, use of multiple codes, multiplemodulation formats, or time-sequential selection of operating mode.

The following illustrate application of aspects of the presentinvention, for particular modulation schemes.

One embodiment of the invention includes a telephone whose first modecomprises analog voice techniques and traditional cellular frequencydivision multiplexed operation employing, but not limited to, narrowbandradio frequency modulation techniques, such as FM, and whose second modecomprises microcellular operation including, but not limited to, digitalvoice commanding and/or compression techniques coupled with spreadspectrum radio frequency modulation, and/or time and/or frequencydivision multiplexing techniques, where the cellular and microcellularmodes occupy common frequency bands. The microcellular mode also mayinclude a paging function, which may utilize narrowband or spreadspectrum technologies, and occupy frequency bands common to the cellularand microcellular modes, or may be offset from both or either, and maybe independent of the unit's telephone functionality.

Another embodiment of the invention includes a telephone whose firstmode comprises cellular frequency division multiplexed operationemploying, but not limited to, narrowband radio frequency modulationtechniques, such as FM, coupled with digital voice commanding and/orcompression and/or time division multiplexing techniques, and whosesecond mode comprises microcellular operation including, but not limitedto, digital voice compendium and/or compression techniques coupled withspread spectrum radio frequency modulation, and/or time and/or frequencydivision multiplexing techniques, where the cellular and microcellularmodes occupy common or distinct frequency bands. The microcellular modemay also include a paging function, which may utilize narrowband orspread spectrum technologies, and may occupy frequency bands common tothe cellular and microcellular modes, or may be offset from both oreither, and may be independent of the unit's telephone functionality.

It will be apparent to those skilled in the art that variousmodifications can be made to the described transmitter and receiverconfigurations without departing from the scope or spirit of theinvention, and it is intended that the present invention covermodifications and variations of the techniques shown herein providedthat they come within the scope of the appended claims and theirequivalents.

As previously noted with respect to FIG. 1, a spread-spectrum signal 6may have a spreading bandwidth which exceeds the bandwidth of the inputdata 3. The spread-spectrum signal 6 may also be modulated onto acommunication channel having a center frequency, with the centerfrequency and the spreading bandwidth substantially defining acommunication channel, and the communication channel may have a knownsignal dropoff for energy outside the limits of the channel. It has beenfound by the inventors that a particular set of selected values for thespreading bandwidth and the center frequency provide a substantial andsurprising advantage when using spread-spectrum techniques for wirelesscommunication.

In particular, it has been found by the inventors that a spreadingbandwidth of about 10 megahertz (MHz) or less offers several advantagesin spread-spectrum wireless communication. These advantages include:

minimizing interference with microwave communication users whentransmitting in a microwave communication band such as the 1850-1990 MHzcommunication band;

minimizing interference with, and maximizing compatibility with,cellular communication users when transmitting in a cellularcommunication band such as the cellular communication bands near 800-900MHz and other cellular communication bands;

mitigating the effect of frequency-selective fading when transmittingusing a spread-spectrum technique;

allowing the same spread-spectrum technique to be used in othercommunication bands, such as the 90-928 MHz band and the 2400-2483.5 MHzband; and

other and further advantages which are detailed in, and which wouldappear from, the technical appendix to those of ordinary skill in theart, after perusal of the specification, drawings and claims.

Using a 10 MHz or smaller band for spread spectrum communication whentransmitting within a microwave communication band (such as the1850-1990 MHz communication band) minimizes interference with microwavecommunication users in several ways. As a general matter, interferenceavoidance is a function of both geography and frequency selection.Typically, microwave communication is directed over a beampath between amicrowave transmitter and receiver. Because microwave stations providecritical services such as, for example, controlling the nation'selectric power grid, the possibility of inadvertent disruption of suchservices extremely serious. Accordingly, government regulationstypically require that microwave stations such as licensed OFS receiverscannot be required to tolerate more than a set level (e.g., 1 dB) ofinterference in their areas of operation. Users of the microwavefrequency bands within the geographic area of licensed microwavestations therefore cannot operate in a zone which would cause more than1 dB of interference to the microwave station. This zone may be referredto as an exclusion zone.

FIGS. 4 and 5 show examples of exclusion zones for a specifictraditional narrowband communication technique as compared to a specifictype of spread spectrum communication technique. FIG. 4 compares thesize of exclusion zones 331 and 332 around a microwave beampath 330under a theoretical freespace loss model. As can be seen in FIG. 4, theexclusion zone 332 for narrowband communication may be far larger thanthe exclusion zone 331 for spread spectrum communication. It can also beseen that the exclusion zones 331 and 332 extend farthest in thedirection of the beampath 330. With respect to other directions, theexclusion zones 331 and 332 extend relatively farther out at 90 degreesto the beampath 330, but are relatively closer, for example, in thedirection opposite the beampath 330 and at various other angles asdepicted in FIG. 4.

In a similar manner, FIG. 5 compares the size of exclusion zones 341 and342 around a microwave beampath 340 under a HATA loss model (median citysuburban assumption). The exclusion zones 341 and 342 for FIG. 5,although derived from a different loss model, are similar in shape tothose of FIG. 4.

Because of the particular shape of the exclusion zones 331, 332, 341 and342 (as illustrated in FIGS. 4 and 5), minimizing interference withmicrowave communication users may potentially be achieved by avoidanceof the microwave beampath 330 or 340. It has thus far, however, beenunappreciated that OFS avoidance is more difficult for signals, be theynarrowband or spread spectrum signals, exceeding 10 MHz in bandwidth orextending over multiple OFS bands. The reason for such difficulty stemsfrom the fact that approximately 94 percent of all OFS links are 10 MHzlinks. Thus, while it might be possible to select a 10 MHz band on whichto transmit so as to interfere with at most only a single 10 MHz OFSlink, any signal wider than 10 MHz could potentially interfere with atleast two and possibly more OFS links. This problem is exacerbated bythe fact that, in and around many urban areas, OFS microwave beampathsof different frequency bands may not necessarily be parallel but mayintersect in a variety of patterns. Thus, the existing geographicpattern of microwave links in most major cities would necessitate that,in many if not most cells (in the case of a cellular system), any signalwider than 10 MHz transmitted in microwave frequency bands wouldinterfere with the beampath of more than one microwave station no matterhow much frequency avoidance was employed.

In contrast, the present invention provides in one embodiment means foravoiding or minimizing interference with existing OFS links by selectionof a particular frequency bandwidth for spread spectrum communication.In particular, this aspect of the present invention provides for aspread spectrum communication bandwidth that is 10 MHz or less in size.Given a known allocation of frequency bands for OFS users, the presentinvention in one embodiment allows for selection of a 10 MHz or smallerband for spread spectrum communication so as to avoid the beampath ofexisting fixed microwave users or, in the worst case, to potentiallyinterfere with only a single microwave communication user. For example,if the selected band for spread spectrum communication is coextensivewith or entirely within the bandwidth of a known 10 MHz OFS link, then,because OFS channels are frequency multiplexed, the spread spectrumcommunication signal can interfere with at most the one known 10 MHzlink. Further, the spread spectrum transmitter 1 can be geographicallylocated so as to minimize or avoid interference with that existing OFSlink.

Another way in which aspects of the present invention minimizeinterference with microwave communication users is by using a spreadspectrum signal for communication. A spread-spectrum signal with itsnoise-like characteristics creates much less interference than anarrowband signal of comparable power. Approximately 83% of all OFSlinks use analog microwave systems which are highly susceptible tonarrowband interference. The maximum allowable interference to amicrowave receiver is commonly defined by the TSB10E standard as only a1 dB rise in the receiver's noise threshold. A 10 MHz bandwidth spreadspectrum signal may result in 1/100 (20 dB) less interference to an OFSreceiver compared with a similar power 100 KHz bandwidth narrowbandsignal. The difference in interference is illustrated, for example, inFIGS. 4 and 5. FIG. 4 compares the exclusion zone 332 (assuming a 2 GHzmicrowave transmitter having a directional antenna at a height of 200feet) of a 100 KHz narrowband signal with the exclusion zone 331 of a 10MHz spread spectrum signal using a theoretical freespace loss model. Thenarrowband exclusion zone is 30 to 100 times larger than the spreadspectrum exclusion zone. FIG. 5 shows a similar comparison using a HATAloss model (median city suburban assumption).

A further advantage of using a 10 MHz or smaller spread spectrumcommunication bandwidths is that it provides an easy migration path intothe existing bands of OFS users if the OFS users can be relocated toanother band.

Information relating to construction of a spread-spectrum communicationsystem using a 10 MHz or less spreading bandwidth and having knowncenter frequencies may be found in detail in the technical appendixincorporated by reference fully herein. The specification, drawings,claims, and the technical appendix, in combination, contain a writtendescription of the invention, and the manner and process of making andusing it, in such full, clear, concise and exact terms as to enable anyperson skilled in the art to make and use the same.

For example, a spread spectrum system for communicating over a 10 MHz orsmaller frequency band may be part of a cellular network. The system maycomprise a plurality of base stations 381 arranged in an approximatelytriangular grid 383 covering a service area, as shown in FIG. 6. Regionssurrounded by three base stations 381 may comprise triangular cells 380.Each base station 381 may consist of six transmitters, each separatelydriving a 60° sector antenna. For aesthetic reasons, conformal mount,flat antennas mounted on the sides of buildings may be used in someareas where obtaining zoning for tower mounted antennas is difficult oreconomically undesirable. Although not required, the frequency of eachtransmit sector can be different if necessary to minimize interferencewith existing OFS and PCS services. The data transmission rate may beindependently set from cell to cell; that is, different sectors of abase station may transmit at different rates.

A triangular service cell 380 is shown in FIG. 7. Three base stations381 having transmitters form the corners of the triangular service cell380. The base stations 381 send high speed data using appropriate 60°antennas and may also use different spreading codes and/or differentfrequencies. Because different frequencies may be used, the describedsystem allows for OFS frequency avoidance on a cell sector by cellsector basis. Within the data stream, block interleaving andconvolutional encoding may also be used to further mitigate fading andinterference effects. An additional low rate base state/sectoridentifier data stream, unique to each transmitter, is employed tofacilitate mobile unit location determination and data transmissionquery processing.

In one configuration, the data on the outbound transmission in eachtriangular cell 380 may be different. Because each transmitter can alsouse a different spreading code, at a receiver 382 the signals can beseparated and processed independently prior to data system combining. Asshown in FIG. 7, the receiver 382 within a triangular cell 380 may be ina position to receive signals from at least three base stations 381. Thereceiver 382 independently despreads the three signals, performs softdecision data demodulation, and combines the data streams prior toconvolutional decoding. Code based, variable delays may be introduced tosynchronize data streams prior to combining.

The base stations 381 may be synchronized using a global positioningsystem. By including base station position in the data stream, a usercan determine his or her location to an accuracy of about 30 feet bymeasuring pseudorange to each of the three transmitters located at thebase stations 381. The user can also obtain timing information within anaccuracy of about 30 to 100 nanoseconds.

The above described system employing triple transmission and spreadspectrum communication has several important advantages. The systemsignificantly reduces sensitivity to signal shadowing effects caused bybuildings, hills, and similar obstacles. The system mitigates multipathfading effects and enhances error correction coding performance.Further, if interference is encountered at one frequency, a signal maybe transmitted at a different frequency by one of the other two basestations 381 of the triangular cell 380. Also, the system architecturereduces required transmit power and, consequently, reduces the potentialfor OFS interference. Low power transmitters (e.g., as low as 100 mW)may be used in regions where OFS interference exists.

When base stations 381 are located close together, the maximum datatransmission rate is determined primarily by mutual interferenceconsiderations, while at wider separations of base stations 381, thedata transmission rate is limited by noise. Even in areas near an OFSuser on the same frequency, a triangular grid of transmitters 1 to 2 kmapart may provide 600 kbit/s raw data rate at a bit rate error of 10⁻⁶.A compact receiver may be capable of combining multiple simultaneous 1.5Mbit/s transmissions in a single contiguous 10 MHz band of sharedspectrum. The receiver may have the option of selecting any of theavailable transmission frequencies based on local propagationcharacteristics and received S/(1+N). A user experiencing good qualityreception may request a higher data rate if total traffic warrants.

The system for transmitting spread spectrum signals over a 10 MHzbandwidth may employ time division multiplexing or duplexing in order toseparate users. Time separation avoids interference problems, as theinterference in any single time slot is simply that created by a singleuser. Thus, multiple users could share the same 10 MHz bandwidth whilecreating the interference of only a single continuous user. In contrast,in other systems the aggregate interference per cell typically risesproportionally with the number of users leading to interference problemswith OFS and other users sharing the electromagnetic spectrum. Timedivision multiplexing or duplexing may be combined with frequencydivision multiplexing or duplexing in order to increase the number ofseparate users.

Another aspect of the invention relates to a technique forspread-spectrum communication which uses more than one frequency band,particularly frequency bands including the 902-928 MHz, 1850-1990 MHz,and 2.4-2.4835 GHz frequency bands. As noted above, the spread-spectrumsignal 6 may be modulated onto a communication channel. Thecommunication channel may be selected from frequencies in one of aplurality of frequency bands, including the 902-928 MHz, 1850-1990 MHz,and 2.4-2.4835 GHz frequency bands, and including the 1910-1930 MHzfrequency band or other future unlicensed frequency bands, or otherdesignated frequency bands.

In this aspect of the invention, a spreading bandwidth of 10 MHz may beused, or a different spreading bandwidth which may be more or less than10 MHz. A different spreading bandwidth may be used from time to time; adifferent spreading bandwidth may be used for communication in differentfrequency bands, or for different uses.

In a preferred embodiment, the invention provides for changing thefrequency band onto which the spread-spectrum signal 6 is encoded upon achange in environment or other control trigger. For example, the 902-928MHz and 2.4-2.4835 GHz bands may be used for private accessspread-spectrum communication, such as with a PBX, PABX, residentialtelephone, key system, Centrex system, or other related system, whilethe 1850-1990 MHz band may be used for public access spread-spectrumcommunication, such as public telephone access. In a preferredembodiment, a spread-spectrum transmitter 1 may be embodied in a handset13 and may dynamically switch from one frequency band to another basedon whether it is able to access a local PBX or PABX 14 viaspread-spectrum communication. In particular, the handset 13 may becapable of switching between the 1850-2200 MHz band and the 2400-2485MHz band, or between two sub-bands within those bands. In place of thePBX or PABX 14, a related system such as a residential telephone, keysystem, or Centrex system may be readily substituted. Alternatively, thetransmitter 1 may dynamically switch from one frequency band to anotherbased on local propagation characteristics and received S/(1+N).

FIG. 8 shows one possible scheme for dividing the 1850-1990 MHz and2400-2485 MHz bands into sub-bands of 10 MHz or 5 MHz each. A firstbandwidth 400 comprising frequencies from 1850-1930 MHz may be dividedinto sub-bands 402 of 10 MHz or 5 MHz each. Thus, if the first bandwidth400 is divided into sub-bands 402 of 10 MHz, then eight channels couldbe provided, while if divided into sub-bands 402 of 5 MHz, then sixteenchannels could be provided. Likewise, a second bandwidth 405 comprisingfrequencies from 2400-2480 MHz may be divided into sub-bands 406 of 10MHz or 5 MHz each. A dual mode phone 410 provides access to a select oneof the plurality of sub-bands 402 in the first bandwidth 400, and may beswitched to provide access to a select one of the plurality of sub-bands406 in the second bandwidth 405.

While transmitting in a sub-band 402 within the first bandwidth 400,which comprises licensed frequency band to which OFS users would haveaccess, the dual mode phone 410 may transmit using spread spectrumcommunication taking advantage of CDMA and/or TDMA methods in order tominimize interference with OFS microwave users. If no OFS user ispresent, the dual mode phone 410 may of course transmit usingconventional narrowband techniques. While transmitting in a sub-band 406within the second bandwidth 405, which comprises unlicensed frequenciesavailable to PCS systems such as PBX, Centrex or other systems, the dualmode phone 410 may transmit using spread spectrum communication takingadvantage of CDMA and/or TDMA methods in order to minimize interferencewith existing users, if any, or may transmit using conventionalnarrowband techniques. Thus, the same dual mode phone 410 may access acellular system, for example, in a first bandwidth 400 but, by operationof a switch, may access a private access network such as a PBX orCentrex in a second bandwidth 405.

FIG. 9 shows a similar scheme for communicating in either one of twodifferent frequency bands.

Information relating to construction of a spread-spectrum communicationsystem which uses more than one frequency band, particularly frequencybands including the 902-928 MHz, 1850-1990 MHz, and 2.4-2.4835 GHzfrequency bands may be found in detail in the technical appendixappended hereto, incorporated by reference herein in its entirety, aswell as in the description set forth earlier herein. The specification,drawings, claims, and the technical appendix, in combination, contain awritten description of the invention, and the manner and process ofmaking and using it, in such full, clear, concise and exact terms as toenable any person skilled in the art to make and use the same.

For example, FIG. 10 shows a dual-mode spread-spectrum modulator withtwo frequency bands. The dual-band spread-spectrum modulator uses asingle, relatively narrow, synthesizer to serve two operating frequencybands. In the lower frequency band, the synthesizer may operate in ahigh-side injection mode, while in the higher frequency range, thesynthesizer may operate in a low-side injection mode. In a preferredembodiment, the lower frequency range may comprise about 1850 to 1990megahertz, while the higher frequency range may comprise about 2400 to2483.5 megahertz.

The operation of the device shown in FIG. 10 will now be explained inmore detail. A first frequency source 401 may generate a first frequencyf1 402, while a second frequency source 403 may generate a secondfrequency f2 404. The first frequency f1 402 and the second frequency f2404 may be coupled to a multiplier 405, which may generate a bimodalsignal 406 with a frequency distribution over two frequency ranges fL407 and fH 408. In a preferred embodiment, the lower of the twofrequencies fL 407 (fL=f1-f2) may range from about 1850 to1990megahertz, while the higher of the two frequencies fH 408 (fH=f1+f2)may range from about 2400 to 2483.5 megahertz. When one of the twofrequencies f1 and f2, e.g., f2 is chosen between the two ranges, e.g.,about 2200 megahertz, the other frequency, e.g., f1 may be chosenbetween about 300 and 440 megahertz.

The bimodal signal 406 may be coupled to a binary encoder 409, forencoding a data stream 410. The data stream 410, comprising a sequenceof data bits 411, may be coupled to the binary encoder 409, which maygenerate a first frequency, e.g., fL 407, when a data bit 411 in thedata stream 410 is a "0" bit, and may generate a second frequency, e.g.,fH 408, when a data bit 411 in the data stream 410 is a "1" bit.

The present invention also provides for monitoring a frequency in eachband (or transmitting to a frequency in each band) at once, because both(f1+f2) and (f1-f2) can be stepped down to the same intermediatefrequency with a single local oscillator. When the intermediatefrequency is 260 MHz and the local oscillator is set to 2180 MHz, thepresent invention allows operation at both 1920 MHz and 2440 MHz. Whenthe local oscillator is set 10 MHz greater, the present invention thenallows operation at both 1930 MHz and 2450 MHz, i.e., two frequencieseach 10 MHz greater. Thus, for paired frequencies, the present inventionallows reception or transmission on either frequency (or both) in thepair.

FIG. 11 shows a programmable frequency generator.

A reference frequency signal 501 may be coupled to a multiplier 502. Themultiplier 502 may generate a signal f(s) 503, which may be coupled to avoltage-controlled oscillator (VCO) 504. The VCO 504 may be coupled toan output node 505, which provides an output frequency signal 506, andmay also be coupled in a feedback configuration to the multiplier 502 byway of a programmable divide-by-N counter 507. The programmabledivide-by-N counter 508 may be programmed by a set of control lines 509.In one embodiment, the divide-by-N range of the programmable divide-by-Ncounter 507 comprises 23 steps, from 205 to 234.

FIG. 12 is an alternative embodiment of a transmitter using a singlefrequency synthesizer for communicating over a plurality of frequencybands. In FIG. 12, an incoming data stream 601 to be modulated isprovided to a spread spectrum encoder 602, which encodes the data stream601 and outputs a spread spectrum signal 605. The spread spectrumencoder 602 may encode the data stream 601 by modulating it with a PNcode, or by employing an M-ary spread spectrum technique. The spreadspectrum signal 605 is connected to a modulator 609. A carrier signalhaving a frequency f1 is generated from a signal source 603 and is alsoconnected to modulator 609. Modulator 609 outputs a modulated spreadspectrum signal 607.

The modulated spread spectrum signal 607 is connected to anothermodulator 610. A frequency synthesizer 606 (e.g., such as shown in FIG.11) generates a programmable frequency signal 608, which is alsoconnected to the modulator 610. The programmable frequency signal 608has a center frequency of fn, which may be programmed by control lines509 such as shown, for example, in FIG. 11. Modulator 610 outputs abimodal signal 611 having frequency components at frequencies f1+fn andf1-fn.

The bimodal signal 611 is connected to a wideband amplifier 615. Thewideband amplifier 615 is controlled by a band select signal 616, whichcauses the wideband amplifier 615 to perform at an operating pointtailored for either the frequency f1+fn or the frequency f1-fn. Anoutput of the wideband amplifier 615 is connected to two bandpassfilters 619 and 620. One bandpass filter 619 has a center filteringfrequency of f1+fn, and the other bandpass filter 620 has a centerfiltering frequency of f1-fn. The first bandpass filter 619 passes theportion of the amplified signal having frequency components at f1+fnwhile attenuating the frequency components at f1-fn, and the secondbandpass filter 620 passes the portion of the amplified signal havingfrequency components at frequency f1-fn while attenuating the frequencycomponents at frequency f1+fn. Bandpass filter 619 outputs an outputsignal 622 having a frequency f1+fn, while bandpass filter 620 outputsan output signal 623 having a frequency f1+fn.

Thus, the FIG. 12 transmitter allows generation and transmission, usinga single frequency synthesizer 606, of a signal in either or both of twofrequency bands, wherein the frequency f1+fn lies in one frequency bandand the frequency f1-fn lies in the other frequency band. FIG. 15 is adiagram of frequency bands and sub-bands illustrating frequency pairsthat may be generated for a selected f1 and fn. In FIG. 15, a pair offrequency bands F_(H) and F_(L) are each divided into a plurality ofsub-bands 750. The higher frequency band F_(H) is divided into sub-bandsSBH1, SBH2, . . . SBHN, while the lower frequency band F_(L) is dividedinto sub-bands SBL1, SBL2, . . . SBLN. The sub-bands SBH1 . . . SBHN andSBL1 . . . SBLN are paired, with the highest of the sub-bands SBH1 inthe high frequency band F_(H) paired with the lowest of the sub-bandsSBL1 in the low frequency band F_(L), the second highest of thesub-bands SBH2 in the high frequency band F_(H) paired with the secondlowest of the sub-bands SBL2 in the low frequency band F_(L), and so on,until the lowest of the sub-bands SBHN in the high frequency band F_(H)is paired with the highest of the sub-bands SBLN in the low frequencyband F_(L), thereby resulting in frequency pairs PAIR-1, PAIR-2, . . .PAIR-N. The high frequency band F_(H) may comprise all or a portion ofthe band ranging from 1850 MHZ to 1990 MHZ, while the low frequency bandF_(L) may comprise all or a portion of the band ranging from 2.4 MHZ to2.485 MHZ. The sub-bands SBH1 . . . SBHN and SBL1 . . . SBLN need not becontiguous within each of the main frequency bands F_(L) and F_(H).

In operation, the programmable frequency synthesizer 606 is programmedto select a frequency fn, preferably selected from one of a discretegroup of N frequencies corresponding to the frequency pairs PAIR-1,PAIR-2, . . . PAIR-N. The largest selected fn allows operation over thefrequency sub-band pair denoted PAIR-1, while the smallest selected fnallows operation over the frequency sub-band pair denoted PAIR-N, withthe frequency selections for fn between the smallest and largest valuesof fn corresponding to frequency pairs PAIR-2 through PAIR-(N-1). Thus,by changing the frequency fn in discrete steps, the transmitter of FIG.12 can be operated over a different pair of frequency sub-bands 750.

While the FIG. 12 embodiment is described with the frequency f1 greaterthan frequency fn, it is also possible to have frequency fn be greaterthan frequency f1. In such a case, the relative frequency differencebetween the higher frequency signal at a frequency fn+f1 and the lowerfrequency signal at a frequency fn-f1 will be a constant 2·f1 as thefrequency fn is varied according to control lines 509 or otherprogramming means.

FIG. 13 is another embodiment of a transmitter using a single frequencysynthesizer for allowing communication over a plurality of frequencybands. In FIG. 13, a data stream 651 is encoded by a spread spectrumencoder 652 in a similar manner to FIG. 12. A spread spectrum signal 655output from the spread spectrum encoder 652 is modulated with a carriersignal 654 from a signal source 653 by modulator 659. The carrier signal654 has a frequency f1. The modulator output 657 is connected to anothermodulator 660. A frequency synthesizer 656 (e.g., such as the one shownin FIG. 11) generates a programmable frequency signal 658, which is alsoconnected to the modulator 660. The programmable frequency signal 658has a center frequency of fn, which may be programmed by control lines509 such as, for example, shown in FIG. 11. Modulator 660 outputs abimodal signal 611 having frequency components at frequencies f1+fn andf1-fn.

The bimodal signal 661 is connected to two narrowband power amplifiers670 and 671. One narrowband power amplifier 670 is configured to operateat a frequency of f1+fn, while the other narrowband power amplifier 671is configured to operate at a frequency f1-fn. Outputs from each of thenarrowband power amplifiers 670 and 671 are provided to an analogmultiplexer 675 (or a set of switches), which selects one of the twooutputs from amplifiers 670 and 671 in response to a band select signal676. The multiplexer 675 may be configured so that it selects one orboth of the amplifier outputs, thereby allowing operation over a singlefrequency band or two frequency bands, and in either case using a singlefrequency synthesizer 656. The FIG. 13 transmitter operates over pairedfrequency sub-bands SBH1 . . . SBHN and SBL1 . . . SBLN (see FIG. 15) ina manner similar to the FIG. 12 transmitter, depending on the frequencyfn selected for the programmable frequency signal 658.

FIG. 14 is a block diagram of a receiver for receiving and demodulatingsignals that may be sent over two frequency bands. In the FIG. 14receiver, a transmitted signal 703 is received by an antenna 700 andprovided to a switch 709. In one position A, the switch 709 connects toa first bandpass filter 714 having a center filtering frequency off_(IF) +fn, while in another position B, the switch 709 connects to asecond bandpass filter 715 having a center filtering frequency of f_(IF)-fn. In a preferred embodiment, frequency f_(IF) is selected asfrequency f1 used in the transmitter.

Outputs from each of the bandpass filters 714 and 715 are connected toanother switch 710. In a first position A, the switch 710 connects tothe first bandpass filter 714, while in another position B, the switch710 connects to the second bandpass filter 715.

Switches 709 and 710 are controlled by a band select signal 719. Whenthe switches 709 and 710 are set in position A, the FIG. 14 receiver isconfigured to detect signals sent over a frequency band centered atf_(IF) +fn, and when the switches 709 and 710 are set in position B, thereceiver is configured to detect signals sent over a frequency bandcentered at f_(IF) -fn. While two switches 709 and 710 are shown in FIG.14, the same result may be achieved by using only a single switch 709 or710. A variety of other selection means could also be utilized.

The output from switch 710 is connected to a multiplier 720. A frequencysynthesizer 721 generates a programmable frequency signal 722 having afrequency fn. The programmable frequency signal 722 is also connected tothe multiplier 720. The frequency fn is selected to match the desiredfrequency sub-band pair PAIR-1, PAIR-2, . . . or PAIR-N, and thereforecan monitor either of the two sub-bands 750 comprising the pair,depending on the setting of the band select signal. By switching thefrequency fn of the programmable frequency signal 722, the FIG. 14receiver can be adjusted to monitor two other frequency sub-bands 750.The sub-bands 750 that can be monitored by changing frequency fn havethe same pattern as shown in FIG. 15--that is, the highest sub-band SBH1in the high frequency band F_(H) is paired with the lowest sub-band SBH1in the low frequency band F_(L), and the lowest sub-band SBHN in thehigh frequency band F_(H) is paired with the highest sub-band SBLN ofthe low frequency band FL.

By replacing switches 709 and 710 with a connection to both the A and Bpositions, the FIG. 14 receiver can be modified to simultaneouslymonitor two frequency bands, i.e., the frequency bands centered atfrequencies f_(IF) +fn and f_(IF) -fn.

Multiplier 720 outputs a downconverted signal 725. The downconvertedsignal 725 is provided to an IF/demodulation block 730, whichdemodulates the downconverted signal 725 to recover the originalinformation modulated thereon. The demodulation block 730 operates atthe frequency f_(IF) (i.e., f1), and may comprise a frequency source forgenerating a frequency f1, and/or a spread spectrum decoder anddemodulator.

As with the dual-band transmitters previously described, the frequencyfn in the dual-band receiver of FIG. 14 may be selected as larger thanthe frequency f1, in which case the bandpass filter 714 may beconfigured to have a center filtering frequency of fn+f_(IF), andbandpass filter 715 may be configured to have a center filteringfrequency of fn-f_(IF). Thus, the frequency sub-bands to be monitoredwould be separated by a fixed 2·f_(IF) as the frequency fn is variedamong its programmable frequency values.

Alternative Embodiments

While preferred embodiments are disclosed herein, many variations arepossible which remain within the concept and scope of the invention, andthese variations would become clear to one of ordinary skill in the artafter perusal of the specification, drawings and claims herein.

For example, information which is encoded for transmission isoccasionally referred to herein as "data", but it would be clear tothose of ordinary skill in the art, after perusal of this application,that these data could comprise data, voice (encoded digitally orotherwise) error-correcting codes, control information, or othersignals, and that this would be within the scope and spirit of theinvention.

What is claimed is:
 1. An apparatus for multi-band multi-modecommunication comprising:a transmitter having a plurality oftransmission modes and a plurality of modulators; a receiver having aplurality of demodulators; a first and second mode selection signalcoupled respectively to said transmitter and said receiver; a first andsecond filter coupled respectively to said plurality of modulators andto said plurality of demodulators; and said plurality of modulatorscomprising a spread spectrum modulator and a narrowband modulator,wherein said transmitter is capable of transmitting a spread spectrumsignal and a narrowband signal.
 2. The apparatus of claim 1 furthercomprising a plurality of reception modes comprising a communicationsprotocol selected from the group consisting of: AMPS, GSM, IS-45, IS-95and DECT.
 3. The apparatus of claim 1 further comprising a plurality ofinput and output frequency hands comprising a frequency band which spansfrom 2400 megahertz to 2483.5 megahertz.
 4. The apparatus of claim 1further comprising a plurality of input and output frequency bandscomprising a frequency band which spans from 1850 megahertz to 1990megahertz.
 5. The apparatus of claim 1 wherein said receiver andtransmitter are co-located in a mobile handset.
 6. The apparatus ofclaim 1 wherein said plurality of transmission and reception modescomprise a cellular mode.
 7. The apparatus of claim 1 wherein saidplurality of transmission and reception modes comprise a microcellularmode.
 8. The apparatus of claim 1 wherein said plurality of transmissionmodes comprises a communications protocol selected from the groupconsisting of: AMPS, GSM, IS-45, IS-95 and DECT.
 9. The apparatus ofclaim 1 further comprising a paging unit.
 10. An apparatus formuiti-band multi-mode communication comprising:a transmitter comprisingafirst tunable frequency source; a plurality of modulators coupled tosaid first tunable frequency source, said plurality of modulatorscomprising a plurality of transmission modes; a first mode selectionsignal coupled to each of said plurality of modulators; a first filtercoupled to an output of each of said plurality of modulators; saidplurality of modulators comprising a spread spectrum modulator and anarrowband modulator and said transmitter is capable of transmitting aspread spectrum signal and a narrowband signal; and a receivercomprisinga second filter; a second tunable frequency source; afrequency converter coupled to said second filter and coupled to saidsecond tunable frequency source; a plurality of demodulators coupled tosaid frequency converter, said plurality of demodulators comprising aplurality of reception modes a second mode selection signal coupled toeach of said plurality of demodulators.
 11. The apparatus of claim 10wherein said plurality of demodulators comprise a spread spectrumdemodulator and a narrowband demodulator.
 12. The apparatus of claim 10wherein the apparatus is a mobile handset.
 13. The apparatus of claim 10further comprising a mode select switch which selects one of saidplurality of transmission modes.
 14. The apparatus of claim 10 furthercomprising a mode select switch which selects one of said plurality ofreception modes.
 15. The apparatus of claim 10 wherein said transmitterfurther comprises a power amplifier coupled to said plurality ofmodulators, said power amplifier adjustable to operate in each of saidplurality of transmission modes.
 16. The apparatus of claim 10 whereinat least one of said first and second tunable frequency sourcescomprises a programmable frequency synthesizer.
 17. The apparatus ofclaim 16 wherein said programmable frequency synthesizer comprises:areference frequency signal source; a programmable divide-by-N counter; amultiplier having inputs coupled to said programmable divide-by-Ncounter and said reference frequency signal course; and avoltage-controlled oscillator having an input coupled to saidmultiplier, said voltage-controlled oscillator having an output coupledto said programmable divide-by-N counter.
 18. The apparatus of claim 10wherein said first and second tunable frequency sources are the samecomponent shared between said transmitter and said receiver.
 19. Theapparatus of claim 10 wherein said first and second filters are the samecomponent shared between said transmitter and said receiver.
 20. Theapparatus of claim 10 wherein said first filter is capable of passing asignal in each of said plurality of transmission modes.
 21. Theapparatus of claim 10 wherein said second filter is capable of passing asignal in each of said plurality of reception modes.
 22. The apparatusof claim 10 wherein said first and second filters comprise centerfiltering frequencies in a plurality of frequency bands.
 23. Theapparatus of claim 10 wherein at least one of said first and secondfilters comprises an adjustable bandpass filter.
 24. The apparatus ofclaim 10 wherein said first filter comprises a plurality of narrowbandpower amplifiers in parallel, said plurality of narrowband poweramplifiers coupled to a multiplexer.
 25. The apparatus of claim 10wherein at least one of said first and second filters comprises aplurality of bandpass filters in parallel.